138 FOOD INGESTION AND ENERGY TRANSFORMATIONS. 



through the mouth. In a number of instances it was impossible to 

 obtain an accurate measure of the oxygen consumed, owing to careless- 

 ness on the part of the subject in opening the mouth during chewing. 

 This was especially true with the subjects V. G. and J. J. C. On the 

 other hand, F. G. B. and T. M. C. took especial care to prevent such 

 losses and the respiratory quotients found indicate that there was no 

 disturbance and no appreciable leak. Hence we may properly assume 

 that there was an actual increment in the metabolism which was meas- 

 ured with a considerable degree of accuracy. 



The summary of the results of the respiration experiments given in 

 table 68 shows in all cases measurable increases in the metabolism, these 

 varying from 11 to 27 per cent. In the experiments in which the 

 oxygen measurement was lost, due to the carelessness of the subject in 

 opening the mouth while chewing, the carbon-dioxide measurements 

 were used for computing the heat output. The calorific value of carbon 

 dioxide used was the one corresponding to the respiratory quotients 

 found prior to the chewing period, or in the few cases when quotients 

 after the chewing period were available, an average of the two sets of 

 quotients was used. It is of course possible that when the mouth was 

 opened during chewing there was an increase in the carbon-dioxide 

 excretion as a result of an excessive ventilation of the lungs. If this 

 were the case it might account for the increase in the heat output 

 attributed to the chewing, since in these cases the carbon-dioxide pro- 

 duction was the only factor of metabolism available. In the experi- 

 ments with F. G. B. and T. M. C. it is reasonably certain that there 

 was no such loss through the mouth; the heat values could therefore 

 be computed from the oxygen consumption. 



The data secured in the respiration experiments show that as a 

 result of chewing gum the basal metabolism may be increased on the 

 average approximately 17 per cent. The diversity of results in the 

 calorimeter experiments may be partly explained by the fact that the 

 experiments were carried out over a considerable period of time, and 

 the total increment formed a relatively small proportion of the total 

 heat measured. The conclusion is warranted, however, that chewing 

 gum results in a positive increase in the metabolism of from 10 to 17 

 per cent. Although an analysis of the chewing gum shows that from 

 62 to 69 per cent of carbohydrates was present, it is certain that this 

 small amount of gum i. e., 3 to 30 grams had no influence upon 

 the metabolism. 



Supplementary evidence in regard to the work of mastication was 

 obtained in two experiments in which the subjects vigorously chewed a 

 rubber stopper. Both experiments were made with the respiration 

 apparatus, unfortunately with the less reliable subjects J. J. C. and 

 V. G. The increase in the metabolism was essentially the same as 

 that found with the other subjects in the gum-chewing experiments, 



